Thread cutoff device for lockstitch sewing machines



Jan. 28, 1969 WOLF-RUDIGER VON HAGEN 3,424,116

THREAD CUTQFF DEVICE FOR LOCKSTITCH SEWING MACHINES I Fi'led Aug. 24,1966 Sheet of 4 INVENTOR WOL'F- RUDIGER VON HAGEM BY mm,

AITTORNEYS Jan. 28, 1969 WOLF-RUDIGER VON HAGEN 3,

THREAD CUTOFF DEVICE FOR LOCKSTITCH SEWING MACHINES Sheet 2 of 4 FiledAug. 24, 1966 INVENTOR WOLF- RUDJGER VON HAGEN Jan. 28, 1969WOLF-RUDIGER VON HAGEN 3,424,116

THREAD CUTOFF DEVICE FOR LOCKSTITCH SEWING MACHINES Filed Aug. 24, 19661 .Sheet' 3 0f 4 INVENTOR WOLl-- RUDIGER VON HAGEN ATTORNEY 5 BY flhwm,@1 wag Ma Jan. 28, 1969 WOLF-RUDIGEF VON HAGEN 3,

THREAD CUTOFF DEVICE FOR LOCKSTITCH SEWING MACHINES Filed Aug. 24, 1966Sheet 4 Of 4 WOLF-RUDIGER VON HAGEN IGZ Q W yum/MW ATTOIQNEYS UnitedStates Patent 3,424,116 THREAD CUTOFF DEVICE FOR LOCKSTITCH SEWINGMACHINES Wolf-Rudiger von Hagen, Grotzingen, kreis Nurtingen, Germany,assignor to Union Special Maschinenfabrik, G.m.b.H., Stuttgart,Wurttemberg, Germany Filed Aug. 24, 1966, Ser. No. 574,647 Claimspriority, application Germany, Aug. 25, 1965, U 11,982 VIIa 52a; July15, 1966, U 12,900 VIIa 52a US. Cl. 112252 21 Claims Int. Cl. D05!)65/02 ABSTRACT OF THE DISCLOSURE -A thread severing device employable inlockstitch sewing machines is disclosed herein and includes a stationarythread cutter and a swingably mounted thread catcher for engaging theneedle thread loop and the bobbin thread and moving these threads intocutting engagement with the cutter. The thread catcher is swingablymounted for movement into the needle path at the time the needle threadloop is drawn to its maximum size by a needle thread loop taker normallyprovided in lockstitch sewing machines. The thread catcher remains in aposition proximate the loop taker until the loop taker discards theneedle thread loop whereupon the needle thread loop engages the threadcatcher and the thread catcher returns to its initial position drawingthe engaged threads into cutting operation with the cutter.

The invention concerns a cutoff device for the threads of a lockstitchsewing machine having a stationary knife and a thread catcher movablebetween the throat plate and the looptaker.

In known cutolf devices for the threads of lockstitch sewing machines inwhich both threads are cut off underneath the throat plate, a threadcatcher moves into the needle thread loop during the last revolution ofthe machine, catches a limb of the same as well as the bobbin thread anddraws both out a predetermined amount before the threads are cut. Themovement of the thread catcher is controlled by the sewing machine,usually by means of a cam plate, in such a manner that the threadcatcher at a specific moment enters the needle thread loop andsubsequently draws out the threads, which are then cut off before thesewing machine is stopped.

These cutoff devices require an extremely accurate course of themovement of the thread catcher synchronously with the stitch formation,said course of movement requiring a complicated and expensive drivewhich includes a control device. In addition, this cutoif device or,more particularly the thread catcher, requires a relatively large spacebetween the throat plate and the loop taker, wherefore such cutoffdevices, as a rule cannot be used on sewing machines wherein the looptaker is disposed directly below the throat plate in order to obtain anarrangement which is most favorable for the forming of the stitches.

The invention serves the purpose of providing means associated withlockstitch machines for cutting of the threads under the throat plate,and it contemplates solution of the technical problem of creating acutoff device whose course of movement is simple to control, which needslittle space, and, above all, which also can be installed in existingmachines having the looptaker arranged at a small distance beneath thethroat plate.

This problem is essentially solved by timing the movement of the threadcatcher which is directed into the path of the needle above the bobbincase restraining finger, in such manner that the thread catcher movesinto the needle path at the time when the needle thread loop is "icedrawn out to its maximum size, and that it remains in this positionuntil the needle thread loop after being cast 011? from the looptakerhas deposited and drawn itself around the thread catcher and thatthereafter it moves back against the stationary knife.

This course of movement of the thread catcher does not require anyexpensive mechanism, because it is only necessary to place' the threadcatcher into catching position at a predetermined moment of the sewingcycle and to release it again from that position at another moment,whereupon it is retracted to its starting position in a known manner bythe force of a spring. In this position the threads are then cut off.From the fact that the thread catcher does not actually move into theneedle thread loop, but rather the latter is formed around themomentarily stationary thread catcher, it follows that a relativelylarge tolerance is allowed for the timing of the swinging movement ininwardly and outwardly directions. Thus the movement imparting andcontrol means may be of a relatively simple construction. The threadcatcher is preferably actuated by a solenoid which is controlled by acontact bridge, for example, olf the synchonizer of a needle positioningmotor.

A further essential characteristic consists in the fact that the threadcatcher cooperates within reach of the knife, with a clamping surfacefor clamping the end of the thread going to the needle and also that tothe bobbin. The provision of a clamping surface disposed for cooperatingwith the thread catcher eliminates the need for a special pulling out ofthe threads. The cutoff device can be arranged in the immediate vicinityof the loop taker. The clamping of the threads prevents the unthreadingof the needle and insures a certain sewing start. In addition, throughthe clamping of the threads and arrangement of the cutoff device nearthe loop taker, the severed thread ends projecting from the material arekept short, both at the beginning and at the end of the seam.

The thread catcher is preferably mounted swingably on the support of thebobbin case restraining finger. This support of the bobbin caserestraining finger also suitably carries the stationary knife and formsa guiding surface which cooperates with the thread catcher for clampingthe ends of the threads going to the bobbin as well as to the needle. Byvirtue of this arrangement of the thread catcher and the construction ofthe support for the bobbin case restraining finger, said support beingadapted to accommodate the stationary knife and form a guiding andclamping surface, the cutting device becomes particularly simple as itdoes not require a support of its own and may most advantageously beincorporated into existing machines.

The plane of movement of the thread catcher extends suitably through thepath of the thread seizing beak on the hook assembly. The arrangement ofthe plane of movement intersecting or passing through the path of thethread seizing beak is possible due to the course of the movement of thethread catcher in accordance with the invention, because, during thetime when the thread catcher is swung into its loop intercepting orcatching position, the thread seizing beak is outside the path ofmovement of the thread catcher. As a result of this, the loop taker maybe arranged, as usual, in close proximity to the underside of the throatplate or the underside of the feed dog, said arrangement beingparticularly advantageous for the stitch formation especially in highspeed sewing machines.

In another form of the invention, a clearance recess or channel isprovided between the running-on or guiding surface of the bobbincase-retainer finger and the thread catcher for the reception and theunimpeded passage of the thread strands or portions drawn out by thethread catcher and running to the bobbin and to the needle.

Through this development of the cutting off device, the threads, afterbeing cut off, will lie in a clearance or channel which is covered bythe overlying swung-in thread catcher and said thread portions are keptin the desired position. However, the channel is wide enough so that thethread portions can be pulled out from the channel without anyobjectionable resistance. As a result, the desired end of evenly pullingoff the threads at the start of sewing will be achieved, independentlyof the thickness of the thread, and the beginning of the seam with aneven appearance will be accomplished.

In order that the cutting off of ends of the thread at the end of theseam will be kept short, and that sufficient thread be made available atthe start of sewing, thus to guarantee a safe formation of the firststitch, the thread catcher is provided with a cutting edge protruding inthe direction of the cutting knife and which trails the edge of thethread catcher serving to catch and draw out the thread. Through thisdevelopment of the thread catcher, the separation or severing of thethreads takes place close to the stitching hole of the needle plate, andas a result the ends of the thread at the end of the seam are keptshort. By reason of this arrangement of the edge of the thread catcherwhich seizes and draws out the thread a distance ahead of the cuttingedge which is presented for cooperation with the cutting knife, the endsof the thread running to tthe bobbin and to the needle will obtain asufficient length, so that without jammig the ends of the thread, a safeformation of the first stitch will be assured at the start of sewing.

For the purpose af guiding the threads safely into the channel, thethread catcher has been equipped with guiding edges, serving to hold thethreads in a predetermined position as they are being presented to saidchannel.

In order to assure that the threads will properly engage against theguiding edges, a novel arrangement of guiding element has been providedwhich directs the loop of the needle thread which has been drawn aroundthe bobbin case and which has been released by the gripper point, to theguiding edges of the thread catcher. This guide element, according toone design, consists of a spring part attached to a swinging part of thethread catcher, preferably a spring wire which will resiliently engageagainst the carrier of the bobbin case when the thread catcher has beenswung out. This guiding element will, particularly in the case ofstrongly twisted threads, prevent the loop of the needle thread whichbreaks away from the gripper point from being drawn around the grippertail, so that said thread will follow around the guide element and beheld by the latter until it is drawn away through taking-off of thethread. In this way, the strands of the needle thread are directedsecurely against the guiding edges of the swung-out thread catcher.

With the above and other objects in view that will hereinafter appear,the nature of the invention will be more clearly understood by referenceto the following detailed description, the appended claims and theseveral views illustrated in the accompanying drawings.

In the drawings:

FIGURE 1 is a fragmentary vertical cross sectional view taken throughthe bed and throat plate of a lockstitch machine having embodied thereina cutoff device arranged according to the invention.

FIGURE 2 is a plan view illustrating the cutoff device shown in FIGURE1.

FIGURE 3 is a perspective view depicting the thread catcher immediatelyafter the swinging inwardly.

FIGURE 4 is a view similar to FIGURE 3 and showing the needle threadloop intercepted by the thread catcher before the thread catcher swingsback.

FIGURE 5 is a perspective view of the cutoff device shown in FIGURE 3but with the thread catcher in the starting position.

FIGURE 6 is a diagram schematically showing the course of movement ofthe needle, the loop taker and the thread catcher during the lastrevolution of the main shaft of the sewing machine.

FIGURE 7 is an exploded perspective view illustrating a modified form ofcutoff device embodying the invention.

FIGURE 8 is a perspective view illustrating the cutoff device of FIGURE7 with the thread catcher in its swung-out, needle thread interceptingor receiving position.

FIGURE 9 is a view like FIGURE 8 but with the thread catcher swung in,or back to its starting position.

In the practical development of the invention as shown in FIGURES 1through 6 the support 3 of a bobbin case restraining finger 4 isfastened in the usual way on the bed 1 of a lockstitch sewing machine,which bed carries a throat plate 2, said throat plate 2 having needlehole 5 for passage of the needle 6. In addition, a conventional doublerotating lockstitch loop taker 7 is shown, the same being driven by theshaft 8.

According to the present invention, a thread catcher 9 is swingablymounted on the support 3 for the bobbin case restraining finger 4. Thethread catcher 9 consists preferably of a thin plate fastened on a swingarm 11. A projection 10 on the swing arm 11 abuts in the startingposition, limiting the movement of said arm. The swing arm 11 is mountedon a rock shaft 12 extending through and journalled in said support 3for the bobbin case restraining finger 4. Said rock shaft 12 carries atits other end an actuating lever '13, which is coupled to a solenoid(not shown). In addition, there is received on the rock shaft 12 areturn spring 14, whose one end 15 engages said actuating lever 13 andwhose other end 16 abuts a stop pin 17 fastened to said support 3. Thereturn spring 14 is retained on the rock shaft 12 by a retaining ring18, as best shown in FIGURE 1.

A knife 19 is screw-secured onto the support 3. The actual knife edge 21is disposed some distance above a guiding surface 22 of support 3. Ifretracted to its starting position, shown in FIGURE 2, the threadcatcher 9 is guided along said guide surface 22 and enters the open gapbetween the guide surface 22 and the knife 19. The knife 19 preferablyconsists of a resilient steel plate. The side of the thread catcher 9that is turned toward the knife 19 is shaped in such fashion that itenters the gap between the knife 19 and the guiding surface 22 like awedge, displacing said resilient knife 19 upward.

In FIGURE 3 the needle thread loop is shown as being drawn out to itsmaximum size. This position corresponds approximately to the positionsaccording to FIG- URES 1 and 2. At this particular time the threadcatcher 9 swings into the position illustrated, namely, into the regionof the path of the needle or the loop forming area, whereby the needlethread limb going to the last stitch, and the bobbin thread 26 areplaced automatically on that side of the thread catcher that is turnedtowards the knife. The limb 27 of the needle thread loop going to theneedle is placed on the opposite side. The thread catcher 9 remains inthis position until the needle has reached about its highest position,which corresponds approximately to a position of the loop taker 7 asshown in FIGURE 4. Between the two positions shown in FIG- URES 3 and 4,the loop taker 7 has carried the needle thread loop around the bobbinand the loop has, through the take-up of the needle thread, disposeditself around the thread catcher 9.

The thread catcher 9 now swings back into the starting position as shownin FIGURE 5, where it cuts the threads and clamps the bobbin thread 26and the strand 27 of the needle thread loop extending to the needle.This clamping of the threads is of particular importance. The clamped inbobbin thread insures a certain start of the next sewing operation, andin addition, a relatively short bobbin thread end at the beginning ofthe seam. The clamping of the needle thread prevents unthreading of theneedle, because the needle thread is pulled through the thread take-upapproximately at the time of the cutting operation. The needle thread isheld to such length that a sure stitch formation Will result when thesewing operation is resumed and that the projecting end at the beginningof the seam corresponds in length approximately to the projecting end ofthe bobbin thread.

The tension of the needle thread is preferably released during theswinging back of the thread catcher, so that the thread take-up does notdraw the needle thread out of the clamp. After the needle thread take-uphas reached its terminal position, the thread tension is again appliedso the needle thread is not drawn from the spool when the material isbeing removed, but merely the end of the needle thread out of the clamp.

FIGURE 6 is a schematic illustration of the course of the movement ofthe needle, the loop taker and the thread catcher during the lastrevolution of the main shaft of the machine. The movement curve ofneedle a and loop taker b commence at the highest position of theneedle. The thread catcher 9 swings into the path of the needle at Aabout 100 (this meaning 100 of the angular movement of the main shaft)before reaching the terminal position of the needle (high position ofneedle), and remains in this position over the distance A-B to swingback again to the starting position immediately before reaching theterminal position at B.

In the form of the invention illustrated in FIGURES 7 to 9, there isagain a thread catcher 9a swingably mounted on the support or carrier 3aof a bobbin case restraining finger 40. As in the previously describedform, the thread catcher 9a is attached by screw means 30 to a swingingarm 11a, disposed to have its projection a rest against the carrier 3awhen in the starting position, comparable to the illustration in FIGURE2. The arm '11a is swingably mounted in the carrier 3a by means of arock shaft 12a. Also, a knife 19a is screw secured at 31 onto thecarrier 3a, said knife having cutting edge 21a.

In this form of the invention, however, a clearance recess or channel 32is provided in the running-0n or top guiding surface 2201 of the bobbincase restraining finger 4a, the thread catcher 9a being disposed inposition for swinging across said channel. The thread catcher 9a has acutting edge 33 protruding in the direction of the knife 19a and itsedge 21a, said edge 33 being offset from or trailing the edge 34 of thethread catcher 9: as clearly shown in FIGURE 7.

During the drawing out of the threads, the edge 34 serves in seizing anddrawing out the threads. Additionally, the thread catcher 9a is providedwith guide edges 35, 36, as clearly shown in FIGURE 7. A spring wire 37is attached with one end in the swinging arm 11a and it engagesresiliently with the carrier of the bobbin case whenever the threadcatcher 9a has been swung out, as shown in FIGURE 8.

It is to be understood that when the thread catcher 9a is swung intoposition for cutting off the threads, the spring wire 37 will engageagainst the carrier 38 of the bobbin case, and the needle thread, whichhad been drawn out from the needle 6a by the seizing beak of the looptaker 39 into a loop running around the bobbin case, will be engaged bythe spring wire 37 after release by the gripper point 39, as shown inFIGURE 8, as a result of which any looping of said needle thread aroundthe gripper tail 40 will be prevented. The spring wire 37 will hold theloop of the needle thread firmly as shown in FIGURE 8, until it is drawnoff through the taking-off of the needle thread. As a result, the strandor portion 41 of the loop of the needle thread running to the needle,will be directed to the guiding edge 36 and the strand or portion 42 ofthe thread running to the last stitch will be directed to the guidingedge 35 as will be apparent by reference to FIGURE 8, and in thisposition will loop around the thread catcher 911.

When the thread catcher 9a now swings back into its starting position,it will draw the strand or needle thread portion 41 of the threadrunning to the needle into the clearance or channel 32 of the bobbincase restrainer finger 4a, into which channel the thread strand 4'3running into the bobbin and seized by the guiding edge 35 is likewisedrawn. The projecting cutting edge 33 of the thread catcher 9a will runagainst the fixed cutting knife edge 21a and will sever or separate thethreads. The strands or portions 41 and 43 of the needle thread are heldfreely in the channel 32 after separation of the threads and can bedrawn off without resistance.

While preferred forms of the invention have been disclosed in detailherein, it is to be understood that variations in part structure andarrangement may be made without departing from the spirit and scope ofthe invention as defined in the appended claims.

I claim:

1. In a lockstitch sewing machine wherein are included stitch formingmeans including an uprightly reciprocable needle, a throat plate, aseizing beak equipped loop taker and shaft disposed closely beneath thethroat plate and a bobbin case, the combination of thread severing meansdisposed closely adjacent said plate and loop taker, a bobbin caserestraining finger projecting into proximity with said bobbin case formaintaining the position of said bobbin case, a restraining fingersupport mounting said bobbin case restraining finger and including aportion traversing and arched over the axis of said shaft and adjacentthe loop taker and bobbin case, said thread severing means comprising astationary knife mounted on said support, and thread catcher meansswingably mounted on said support for moving above said restrainingfinger into the needle path when a needle thread loop has been drawn outto its maximum size for remaining in said path to catch the needlethread loop upon the casting off of the needle thread loop by said looptaker and for moving back toward the knife to cooperate therewith in athread severing action.

2. The combination defined in claim 1 wherein the restraining fingerpresents a surface engaged in guiding and thread clamping contact withthe thread catcher means.

3. The combination defined in claim 1 wherein the restraining fingerpresents a surface engaged in guiding and thread clamping contact withthe thread catcher means, and wherein the stationary knife is resilientand spaced above the support, said thread catcher means being movableinto wedging engagement between said support and knife.

4. The combination defined in claim 1 wherein the restraining fingerpresents a surface in guidingcontact with the thread catcher means, saidsurface being recessed to receive threads Without clamping action.

5. The combination defined in claim 1 wherein the thread catcher meansincludes independent spaced guide edges each disposed for engaging andholding threads in a predetermined position.

6. The combination defined in claim 1 wherein the restraining fingerpresents a surface engaged in guiding contact with the thread catcher,the knife being resilient and bearing such spaced relation above thesupport that the thread catcher engages in wedging action between thesupport and knife, the thread catcher having thereon a lead-in edgeportion for first entering the space and a spaced trailing cutter edgeportion disposed to thereafter enter the space and engage in threadcutting contact with the knife.

7. The combination defined in claim 1 wherein there is included a springelement carried by the thread catcher swing mounting and having a freeend overlying and engageable with the bobbin case carrier for yieldablyholding a thread loop thereagainst.

8. A thread cutoff device for severing threads in a lockstitch sewingmachine of the type including a reciproca-ble needle, a throat platemounted for cooperation with said needle, a bobbin case, bobbin caserestraining means and loop taker means for passing the needle threadloop around said bobbin case, said cutoff device comprising threadcutting means mounted proximate said loop taker, thread catcher meansfor catching the needle thread loop upon release thereof from said looptaker means, said thread catcher means being mounted for movement abovesaid bobbin case restraining means, means for moving said thread catchermeans into the path of said needle when said loop taker means draws theneedle thread loop to its maximum size and for returning said threadcatcher means from the path of said needle and into thread cuttingcooperation with said thread cutting means, said bobbin case restrainingmeans further comprising a bobbin case restraining finger and supportmeans mounting said bobbin case restraining finger, said thread catchermeans being swingably mounted upon said support means for swingingmovement into the path of said needle and for return swinging movementaway from the path of said needle.

9. A thread cutofi device according to claim 8- wherein said cuttingmeans comprises a stationary knife mounted upon said support means forthread severing cooperation with said thread catcher upon the return ofsaid thread catcher from the path of said needle.

.10. The cutofl? device according to claim 9 wherein said threadcatching means includes a thread engaging and moving edge and a threadcutting edge projecting toward said cutting knife, said thread engagingand drawing edge projecting beyond said cutting edge toward said cuttingknife to provide thread cutting after said thread engaging and drawingedge has moved past said cutting knife.

11. A cutoff device according to claim 9' wherein said support meanshave formed thereon thread catcher guiding surface means closelyadjacent the path of movement of said thread catcher means for clampingsevered threads against said thread catcher means.

12. A thread cutolf device according to claim 11, said loop taker meansincluding a thread seizing beak movable into engagement with the needlethread loop for passing the loop around a bobbin, said thread catchermeans being mounted for movement in a plane of movement passing throughthe path of movement of said thread seizing beak.

13. The thread cutofi? device according to claim 9, said support meansincluding thread catcher guiding surface means adjacent a portion of thepath of movement of said thread catcher, said guiding surface meanshaving a channel formed therein for the reception of portions of severedthreads to prevent clamping of the received thread portions between saidthread catcher means and said guiding surface means.

14. The thread cutoff device according to claim 13 wherein said guidingsurface means and said channel are provided upon said bobbin caserestraining finger.

;15. In a sewing machine of the type including a throat plate, bobbinsupport means for mounting a bobbin beneath the throat plate and needlethread loop taking means for passing a needle thread loop around abobbin supported by said bobbin support means, the combinationcomprising thread cutting means for engaging and severing the needlethread in the loop thereof and thread catching means normally disposedadjacent said cutting means and spaced from said loop taking means andmovable for engaging the needle thread loop and moving the portion ofthe loop to be severed into engagement with said cutting means, saidthread catching means comprising swingably mounted thread engaging armmeans swingable from an initial position thereof to a second positionproximate said loop taker for receiving the needle thread loop from saidloop taker while in said second position and retractable from saidsecond position to said initial position for carrying the portion of theneedle thread loop to be severed into severing engagement with saidcutting means.

16. The combination according to claim 15 wherein said thread catchingmeans further comprises movement imparting means mechanically connectedto said thread engaging arm means for moving said thread engaging armmeans to the second position thereof proximate the loop taker, formaintaining said arm means in said second position until release of theneedle thread by said loop taker and for returning said arm means tosaid initial position following release of the needle thread by saidloop taker.

17. A thread cutoll device according to claim 15 further comprisingclamping surface means adjacent said thread cutting means for clamping aneedle thread and a bobbin thread upon movement of the threads intocutting engagement with said thread cutting means by said thread catchermeans.

18. The cutoff device according to claim 15, said loop taking meansincluding a thread seizing beak movable into engagement with the needlethread loop for passing the loop around a bobbin, said thread catchingmeans being mounted for movement in a plane of movement passing throughthe path of movement of said thread seizing beak.

19. The cutoff device according to claim 15 wherein said thread catchingmeans includes guide edge means for engaging and holding threads in apredetermined position for the severing thereof.

20. A thread cutoli device according to claim 19 further comprisingneedle thread guide means for guiding the needle thread loop intoengagement with said thread catcher means upon release of the needlethread loop by said loop taker means.

21. A thread cutoff device according to claim 20 wherein said needlethread guide means comprises a resilient spring element attached to andmovable with said thread catcher means for movement into resilientengagement with a portion of said bobbin case restraining means forclamping the needle thread against said portion of said bobbin caserestraining means during positioning of the needle thread in engagementwith said thread catcher means.

References Cited UNITED STATES PATENTS 1,319,668 10/1919 Morris 112-2521,346,814 7/1920 Pifield 1l2252 1,401,973 1/1922 Fifield 1l22521,228,871 6/1917 Barron ll2252 1,395,274 11/1921 Hagelstein 1122523,173,392 3/1965 Hedegaard 1l2-252 3,173,393 3/1965 Adam 112252 HERBERTF. ROSS, Primary Examiner.

